Purpose: Folic acid (FA)-mediated active targeting improves nanocarrier tumor specificity but exposes targeting ligands to the immune system, causing rapid clearance and nonspecific uptake. Existing acid-labile benzoic-imine PEG sheddable systems are insufficiently stable at physiological pH. A more stable, tumor-triggered sheddable PEG stealth is needed to protect FA in circulation and expose it at tumor sites while also promoting intracellular drug release.
Hypothesis: If a dual-functional sheddable mPEG stealth is incorporated into polymeric micelles via a tumor acidic pH-cleavable hydrazone bond and FA is conjugated via a reducible disulfide bond, then the micelles will remain stable at pH 7.4, deshield mPEG at tumor acidic pH to expose FA for active targeting, and undergo intracellular destabilization for enhanced cellular uptake and drug release.
Aims: Synthesize amphiphilic block-statistical copolymers with a dual-functional sheddable mPEG stealth and reducibly conjugated FA. - Prepare a panel of copolymers with three different hydrophilic weight fractions to study structure–property relationships. - Characterize micelle size, stability, pH- and reduction-triggered degradation, and drug release. - Evaluate in vitro cytotoxicity and cellular uptake in FA receptor-overexpressing HeLa cells. - Identify an optimized micelle formulation for enhanced anticancer drug delivery.
Delivery system:
Component: Polymer type; Details: Amphiphilic block-statistical copolymer
Component: Hydrophilic monomer; Details: OEGMA300 (oligo(ethylene glycol) monomethyl ether methacrylate)
Component: Hydrophobic biodegradable monomer; Details: HEMA-g-LA (2-hydroxyethyl methacrylate-g-lactate)
Component: Targeting ligand; Details: Folic acid (FA), conjugated via reducible disulfide bond
Component: Stealth corona; Details: mPEG, linked via tumor acidic pH-cleavable hydrazone bond
Component: Synthesis; Details: ATRP, DCC coupling, click coupling (CuAAC)
Component: Payload; Details: Doxorubicin (DOX)
Component: Nanoparticle type; Details: Self-assembled polymeric micelles
Component: Optimized formulation; Details: P1: mPEG(FA)-P(OEGMA300)₄-st-P(HEMA-g-LA)₄, \(D_h\) ≈ 41 nm
Component: Key feature; Details: Dual-functional sheddable PEG: pH-triggered mPEG deshielding, reduction-triggered FA cleavage, intracellular micelle destabilization
Approach: In vitro only. No in vivo animal studies. - Cell line: HeLa cells (high FA receptor expression). - Drug release: DOX-loaded P1 micelles incubated at pH 7.4, 6.5, and 5.0, with or without 10 mM DTT (reducing agent). - Cytotoxicity: MTT assay. - Cellular uptake: Flow cytometry and confocal microscopy at pH 7.4, 6.5, and 5.0. - Controls: Free DOX, blank micelles, untreated cells. - Replicates: n = 3; Student’s t-test; *p < 0.05 considered significant.
Key methods: Polymer synthesis/characterization: ¹H NMR, FT-IR, SEC-MALS, UV-vis. - Micelle characterization: Dynamic light scattering (DLS) for size and size distribution; transmission electron microscopy (TEM) for morphology. - Drug loading/release: DOX loading content and encapsulation efficiency; cumulative release by dialysis/incubation. - Cytotoxicity: MTT assay; IC₅₀ determination. - Cellular uptake: Flow cytometry (mean fluorescence intensity) and confocal laser scanning microscopy.
Key results: P1 micelles: \(D_h\) = 41 nm, narrow size distribution; stable at pH 7.4. - pH-triggered destabilization: At pH 6.5, size increased from 41 nm to 80 nm after 24 h; at pH 5.0, size increased to 627 nm. - Reduction-triggered destabilization: With 10 mM DTT at pH 7.4, size increased from 41 nm to 94 nm after 24 h. - DOX loading: Loading content 3.6%; encapsulation efficiency 37.0%. - DOX release at 24 h: pH 5.0 = 59.0%; pH 7.4 = 45.8%; pH 7.4 + 10 mM DTT = 71%. - Cytotoxicity (IC₅₀): Drug-loaded P1 micelles = 8.76 µg/mL at pH 7.4 and 5.54 µg/mL at pH 5.0; free DOX = 0.87 µg/mL. - Cellular uptake: At pH 6.5, mean fluorescence intensity was significantly higher than at pH 7.4 (*p < 0.05). At pH 5.0, uptake was substantially greater than at pH 7.4. Blank micelles showed high cell viability.
Interpretation: The authors claim that the dual-functional sheddable mPEG stealth provides protection of FA during circulation, tumor acidic pH-triggered FA exposure for active targeting, and intracellular destabilization for accelerated drug release. The optimized P1 micelles exhibit colloidal stability at physiological pH, enhanced cellular uptake at tumor microenvironment pH, and efficient cytotoxicity at intracellular acidic pH, indicating great potential for anticancer drug delivery.
Limitations: In vitro only: No in vivo biodistribution, tumor targeting, efficacy, or safety data. - Single cell line: HeLa cells only; no primary cancer cells or other tumor models. - No in vivo pharmacokinetics or clearance data. - DTT used as reducing agent: Mimics intracellular reducing environment but not identical to glutathione in vivo. - Serum instability noted: Micelle aggregation occurred at high concentration and in presence of serum, limiting flow cytometry analysis. - No direct proof of FA exposure or FR-mediated uptake: No folate receptor blocking or competitive inhibition studies reported. - No long-term stability, immunogenicity, or repeated-dose toxicity data. - Only DOX tested as payload. - No scale-up or manufacturing data. - Citation details from accepted manuscript: Final published version may differ in minor details.
